A group of Japanese researchers says it has found a new mutation of the Delta coronavirus variant for the first time in Japan.
The team, led by Associate Professor Takeuchi Hiroaki at Tokyo Medical and Dental University Hospital, announced the finding on Monday.
The group says the mutation was discovered in a patient infected with the Delta variant who had visited the institute in mid-August.
They say genetic analysis revealed the N501S mutation.
The group says only eight cases of the mutation have been reported outside Japan.
The N501S mutation resembles the N501Y variation of the Alpha variant first detected in Britain. The team says it is unclear whether the mutation it discovered has any impact on the virus's transmissibility.
The group says it plans to study further.
Takeuchi says full efforts should be made to contain the coronavirus, as the further spread of infections could lead to continued emergence of new variants in the country.
He also called for using genetic analyses to strengthen monitoring of the virus.